In a UMTS (Universal Mobile Telecommunications System) network, for the purposes of improving spectral efficiency and improving the peak data rate, system features based on W-CDMA (Wideband Code Division Multiple Access) are maximized by adopting HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access). For this UMTS network, for the purposes of further increasing high-speed data rates, providing low delay and so on, long-term evolution (LTE) has been under study (non-patent literature 1).
In the third-generation mobile communication system, it is possible to achieve a transmission rate of maximum approximately 2 Mbps on the downlink by using a fixed band of approximately 5 MHz. Meanwhile, in a system of the LTE scheme, it is possible to achieve a transmission rate of about maximum 300 Mbps on the downlink and about 75 Mbps on the uplink by using a variable band which ranges from 1.4 MHz to 20 MHz. Furthermore, in the UMTS network, for the purpose of achieving further broadbandization and higher speed, successor systems of LTE have been under study (for example, LTE-Advanced (LTE-A)). Accordingly, in the future, it is expected that these multiple mobile communication systems will coexist, and configurations (base station apparatus, mobile terminal apparatus, etc.) that are capable of supporting these multiple systems will become necessary.
In the downlink of the LTE system, a CRS (Cell-specific Reference Signal) is defined. This CRS is used to demodulate transmission data, and, besides, used to measure downlink channel quality (CQI: Channel Quality Indicator) for scheduling and adaptive control, and furthermore used to measure an average downlink propagation path state for cell search and handover (mobility measurement). Meanwhile, in the downlink of a successor system of LTE (LTE-A system), a CSI-RS (Channel State Information-Reference Signal) is under study for dedicated use of CSI (Channel State Information) measurement.